﻿#region Copyright information
// 
// Copyright © 2005-2013 Yongkee Cho. All rights reserved.
// 
// This code is a part of the Biological Object Library and governed under the terms of the
// GNU Lesser General  Public License (LGPL) version 2.1 which accompanies this distribution.
// For more information on the LGPL, please visit http://bol.codeplex.com/license.
// 
// - Filename: Permutate.cs
// - Author: Yongkee Cho
// - Email: yongkeecho@gmail.com
// - Date Created: 2012-09-06 11:39 AM
// - Last Modified: 2013-01-25 3:59 PM
// 
#endregion
using System;
using System.Collections.Generic;
using System.Linq;

namespace BOL.Linq
{
    public static partial class Linq
    {
        public static IEnumerable<IEnumerable<TSource>> Permutate<TSource>(this IEnumerable<TSource> source)
        {
            var list = source.ToList();

            if (list.Count > 1)
                return from s in list
                       from p in Permutate(list.Take(list.IndexOf(s)).Concat(list.Skip(list.IndexOf(s) + 1)))
                       select p.Prepend(s);

            return new[] { list };
        }
    }
}
